1. Field of the Invention
The present invention relates to an RFID (Radio Frequency Identification) system and, in particular, to a UHF band RFID system used for short-distance communication between a reader/writer and an RFID tag.
2. Description of the Related Art
As a system for managing articles, an RFID system that establishes, on the basis of a non-contact method, communication between a reader/writer and an RFID tag, and transmits information between the reader/writer and the RFID tag is known. The RFID tag includes an RFIC chip used to process a wireless signal and an antenna used to transmit and receive the wireless signal, and predetermined information is transmitted and received as a high-frequency signal between the antenna of the RFID tag and the antenna of the reader/writer through a magnetic field or a radio wave.
Since the RFID tag is to be attached to an article, a reduction in size thereof is required.
As an RFID system that uses a small RFID tag, for example, a system is disclosed in Japanese Unexamined Patent Application Publication No. 2002-183676 where an RFID tag, in which a minute antenna coil is formed on a wireless IC chip, is utilized and by moving a resonance body including a capacitor and a coil, provided in a leading end portion of a reader/writer, closer to this tag, information is read and written.
However, in the RFID system disclosed in Japanese Unexamined Patent Application Publication No. 2002-183676, when the RFID tag is mounted to a mother substrate, such as printed wiring board, for example, the RFID tag is influenced by a metallic substance, such as another mounted component or a circuit pattern, for example, provided in the printed wiring board, and a communication distance is reduced or no communication is established. In addition, due to the influence of the metallic substance, the resonance frequency of the resonance body deviates and the transmission efficiency of a high-frequency signal is reduced, in some cases. In particular, when a metallic body is located adjacent to a portion in which the RFID tag is disposed, the deviations of the resonance frequency and the reduction in transmission efficiency becomes significant.